In 1996, I made the transition from the world of laboratory science to the business side of laboratory animal science. One of my first projects was to assist a university investigator in a task unrelated to this article. However while at the customer site, I observed light/dark cycle experiments being performed in an adjacent laboratory and was intrigued at the device the investigator had fabricated. The animals were housed in a chamber that completely sealed out the room light. The investigator then could expose the test subject to both light of various wavelengths and varied light/dark cycles. They tested for light seepage by leaving photographic film exposed inside the darkened chamber.

The device worked extremely well and had no light leaks, however the entire chamber was made of plywood and even back in the 1990’s this seemed to be less than optimal. Upon further reflection this device had many faults: a porous easily contaminated surface, no regulated airflow, and unfiltered air and doors that, although sealed from the ambient light, were poorly secured. The need for a controlled environment to perform light/dark cycle experiments was clearly demonstrated.

The next light/dark cycle experiment I saw was conducted in a semi-rigid isolator that had a black plastic cover fitted over the front. In reality it was nothing more than a black trash bag held in place with duct tape. In addition, the isolator had a faulty light switch and no timing device for the chamber light. As would be expected the experiment was less than 100% successful.

Present Day The light/dark cycle cycle chamber has since evolved. Today, the chamber is constructed of black polypropylene on all six sides. Polypropylene is widely used in laboratory animal facilities because it is easily sanitized and resistant to all common cold sterilants. The black polypropylene is completely opaque; light does not penetrate or permeate the interior of the chamber. The door to the chamber is gasketed and sealed for biosecurity, correct airflow, and to prevent light transmission. Two light sources with timers are included which enables the use of different wavelength light and alternating light and dark cycles. Clean air is supplied to the chamber via a blower and HEPA filtered plenums,which keeps the test subjects in a clean controlled environment which helps satisfy IACUC and animal care and use guidelines. The HEPA filters are cartridge type, which is easily replaced, relatively inexpensive, and seldom needs changing. The size of the chamber is customized per the investigators needs, whether it needs to fit one cage or 12 or more cages at the same time. Recent improvements also include baffling the air intake to reduce or eliminate light that can bleed through the air intake/ exhaust ports.

Custom Design Unlike many traditional lab animal products the light/dark cycle chamber isn’t off the shelf. The benefit is that the investigator gets to specify the number of cages to put in the light/dark cycle chamber. This allows investigators to select light/dark cycle chambers that will be optimal for their project.

Often researchers are faced with very limited space on their floor or in their laboratory. The light cycle chamber can be configured to account for whatever space is available by arranging cages in shelving that can be optimized either vertically or horizontally. The chambers can be either table top or on a table with casters to further enhance versatility.

Conclusion In the past, light/dark cycle experiments were likely to take place in areas outside laboratory animal management control. Often these experiments were performed in devices that ran the gamut from poor airflow/no air flow consideration to those that were made of materials which today are consider unsuitable for a laboratory animal environment. The light controlled chambers play a valuable role in instances where light cycle experiments cannot be performed in the core facility. The light/dark cycle chamber today satisfies both the needs of the investigator and the facility manager by providing a clean controlled environment that also serves as the testing apparatus.